Introduction

explodeinstaller: ISO Extraction utility

This extraction utility has been writen to assist in the scripted modification of Slackware install CDs, although it may be useful for other distributions.

It differs from other scripts in that it allows editing of all files including the ramdisk contents without being root, and without resorting to FUSE or ISO mounting, it therefore works on a Mac.

Exploding

Usage is simple. From Python:

import explodeinstaller
explodeinstaller.extract_all("slackware64-14.2-install-dvd.iso", "tmp_iso")

You will see that the contents of the ISO are written to the output directory:

└── tmp_iso
    ├── _EFI_BOOT_initrd.img/
    ├── _EFI_BOOT_initrd.img.spec
    ├── _isolinux_initrd.img/
    ├── _isolinux_initrd.img.spec
    └── isofs/

There will be one 'isofs' subdir and zero or more initrd subdirs. Extracted initrds are prefixed with an underscore '_'.

If for some reason you don't find your initrd here, then you may need to modify the explodeinstaller.py source to change the list of search locations for initrd. Most of the time the initrd will be somewhere like /isolinux/initrd.img.

Modification

If you want to change files in the initrd, just go ahead and edit them.

If you want to add files to the initrd, you need to do two things:

• First you need to add the file to the relevant initrd directory.
• Then, you need to update the spec file.

If you only want to add another directory, device, special file or link, then you only need to update the spec file.

You will see that each initrd directory is accompanied by a corresponding .spec file, in the above example there would be one like this:

bash-5.0$ head tmp_iso/_isolinux_initrd.img.spec 
slink cdrom /var/log/mount 777 0 0
dir bin 755 0 0
slink bin/rm busybox 777 0 0
file bin/gzip tmp_iso/_isolinux_initrd.img/bin/gzip 755 0 0
slink bin/logname busybox 777 0 0
etc....

This format is described in the gen_init_cpio help output, so execute that program without arguments to see the options.

Obviously adding packages is just a matter of placing them in the isofs directory.

Assembly

Once you've made any required changes to your set of files, you're ready to re-assemble. Run:

import explodeinstaller
explodeinstaller.assemble_all("tmp_iso", "slackware_mod.iso")

Any initrd directories will be re-packed into their respective positions in the isofs directory heirarchy. If for some reason you want to actually change the location an initrd gets written to you'll need to edit the hidden file .index in the top level of the exploded directory. You'll see this is a json file indicating meta-data that needs to be stored between execution of the exploder and the assembler. It also determines the compression to be used when re-packing the initrds.